1. Field of the Invention
The present invention relates generally to solenoid driver circuits. More specifically, the present invention relates to a solenoid driver circuit which is adapted for use with the digital magnetic latching solenoids which operate the valves of a digital seawater pump.
2. Description of the Prior Art
Digital magnetic latching solenoids harness residual magnetism that remains in a magnetic material that has been exposed to a magnetic field using this residual magnetic force to control the solenoid. Magnetic latching solenoids include two opposing coils and an armature. Selectively energizing one coil at a time moves the solenoid armature in a back and forth motion to turn a valve on and off. Each coil of the magnetic latching solenoid also provides the electromagnetic field necessary to establish the residual magnetic force in the armature and solenoid housing. When the armature reaches the end of stroke and the coil turns off residual magnetic force holds the armature against the solenoid housing, locking the solenoid in one position without external power.
Residual magnetism in magnetic latching coils generates high latching forces without the disadvantages associated with permanent magnets, such as susceptibility to demagnetization, cracking, sensitivity to temperature changes and low magnetic efficiency.
Because coils in a magnetic latching solenoid are energized only for an instant, heat dissipation is of no concern. As a result the coils use larger wires with fewer turns than in conventional solenoids and have lower resistance and inductance. This allows the coils to handle high current and generate extremely strong magnetic forces without a requirement to overcome spring force which equates to fast actuation.
Although magnetic latching solenoids do not have to overcome a spring force, the latching force must overcome residual magnetism which holds the solenoid's actuator in the previously latched position. The actuator must also overcome residual magnetism from a distance which is equivalent to the solenoid actuator displacement.
As the solenoid material's magnetic permeability increases the residual magnetism increases toward saturation which makes it harder to de-latch the solenoid using only a latching current pulse. Conventional driver circuits use this latching current pulse to de-latch the solenoid's actuator from its current position.
Further, as displacement of the actuator is increased, the latching force must be decreased to de-latch the solenoid's actuator.
Thus, to design a driver for a magnetic-latching solenoid requires the designer to use sophisticated and expensive EM software and to have a thorough understanding of electromagnetic theory. There is also a need for a driver for a magnetic-latching solenoid which balances latching force requirements and solenoid displacement.